The present invention relates to a semiconductor memory device and a method of producing the semiconductor memory device. Particularly, this invention relates to a semiconductor memory device with memory capacitors, such as, a dynamic random-access memory (DRAM) and its production method.
Miniaturization and high integration of semiconductors have been developed. With such development, DRAMs, as one of semiconductor memory devices, are provided with stacked memory capacitors. The memory capacitors consist of a storage node electrode and a cell plate electrode arranged as facing each other via a dielectric film for achieving large practical memory cell capacitance. In other words, the memory cell capacitance is decided according to an area where the storage node and cell plate electrodes face each other.
Japanese Laid-Open Patent No. 1997(9)-17968, for example, discloses a technique for achieving a large storage node electrode surface area of a memory capacitor. It is disclosed that: a storage node electrode is formed so that it expands over a storage node contact hole with a dielectric film formed on the surface of the storage node electrode to cover thereof inside and outside the storage node contact hole; and a cell plate electrode is formed over the storage node electrode also to cover thereof inside and outside the storage node contact hole. This technique achieves a large memory capacitance by increasing an area where the storage node and cell plate electrodes face each other even in the storage node contact hole.
Stacked memory capacitors have, however, had an area which has been reduced with development of miniaturization and integration, whereas a demand for high capacitive storage capability has not been changed. Storage node electrodes must be formed thick enough to have an effective large area where storage node and cell plate electrodes face each other to meet the requirement of high capacitive storage capability under the trend of miniaturization and integration. Thick storage electrodes, however, produce tall memory capacitors that cause big steps between memory cells and peripheral circuitry. These steps generate inadequate photolithography in later processes.
In this respect, Japanese Laid-Open Patent No. 1997(9)-17968 discloses a storage node electrode formed so that it expands over a storage node contact hole as discussed above and since that is essential, this Laid-Open patent cannot avoid the problem of steps formed between memory cells and peripheral circuitry as discussed above. Hence, the technique taught by this Laiden patent cannot meet the requirement of miniaturization and integration in future semiconductor devices.
A purpose of the present invention is to provide a semiconductor memory device, and a method of producing such device with small and low capacitors, however, with a large capacitance to avoid a problem of step formation as discussed above.
The present invention provides a semiconductor memory device comprising: at least an access transistor having a gate and a pair of impurity diffusion layers formed on a semiconductor substrate; and at least a memory capacitor having a storage node electrode and a cell plate electrode, the electrodes being connected to each other via a capacitive insulating layer made of a ferroelectric material, the storage node electrode having a surface covered with the capacitive insulating layer, the storage node electrode being formed in a shape of column on one of the pair of impurity diffusion layers in a hole formed from an inter-layer insulating film covering the access transistor to the one of the pair of impurity diffusion layers, a upper surface of the column not exceeding the inter-layer insulating film, the storage node electrode formed in the hole facing the cell plate electrode via the inter-layer insulating film.
Further, the present invention provides a semiconductor memory device comprising: a semiconductor area formed on a semiconductor substrate; an inter-layer insulating layer deposited on the semiconductor area, the inter-layer insulating layer having a hole thorough which a portion of a surface of the semiconductor area is exposed; a first conductive layer formed in a shape of column in the hole, a upper surface of the column not exceeding the inter-layer insulating film; a capacitive insulating film made of a ferroelectric material, the capacitive insulating film covering the first conductive film in the hole; and a second conductive film being elongated on the inter-layer insulating film, a space between the capacitive insulating layer and a side face of the hole being filled with the second conductive film to cover the first conductive film via the capacitive insulating film in the hole, thus having capacitive coupling with the first conductive film.
Further, the present invention provides a method of producing a semiconductor memory device provided with at least an access transistor having a gate and a pair of impurity diffusion layers, and at least a memory capacitor having a storage node electrode and a cell plate electrode, the electrodes being connected to each other by capacitive coupling via a dielectric film, the method comprising the steps of: forming a first insulating film that covers the access transistor; forming a hole by patterning the first insulating film to expose a portion of a surface of one of the pair of the impurity diffusion layers through the hole; forming a second insulating layer that covers an inner side wall of the hole; forming a first conductive film on the first insulating film so that the hole is filled with the first conductive film via the second insulating film; having the first conductive film remained in the hole by removing the first conductive film on the first insulating film so that the second insulating film is exposed; forming the storage node electrode by removing the second insulating film to form a space between the first conductive film and the inner wall of the hole and having the first conductive film remained so that the storage node electrode is formed in a shape of column on the one of the pair of the impurity diffusion layers in the hole and a upper surface of the column does not exceed the first insulating film; forming the dielectric film made of a ferroelectric material to cover a surface of the storage node electrode; forming a second conductive film on the first insulating film so that the space in the hole is filled with the second conductive film; and forming a cell plate electrode on the first insulating film so that the cell plate electrode covers the storage node electrode via the dielectric film by processing the second conductive film.